Particulate mixtures for forming polycrystalline compacts and earth-boring tools including polycrystalline compacts having material disposed in interstitial spaces therein

ABSTRACT

Polycrystalline compacts include smaller and larger hard grains that are interbonded to form a polycrystalline hard material. The larger grains may be at least about 33 times larger than the smaller grains. An interstitial material comprising one or more of a boride, a carbide, a nitride, a metal carbonate, a metal bicarbonate, and a non-catalytic metal may be disposed between the grains. The compacts may be used as cutting elements for earth-boring tools such as drill bits, and may be disposed on a substrate. A particulate mixture includes a first plurality of grains of hard material having a coating formed over the grains of hard material. The coating comprises at least one of a boride, a carbide, a nitride, a metal carbonate, a metal bicarbonate, and a non-catalytic metal. A second plurality of grains of hard material has a grain size at least 33 times larger than the first plurality.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/257,825, filed Apr. 21, 2014, now U.S. Pat. No. 9,187,961, issuedNov. 17, 2015, which is a continuation of U.S. patent application Ser.No. 13/619,931, filed Sep. 14, 2012, now U.S. Pat. No. 9,085,946, issuedJul. 21, 2015, which is a divisional of U.S. patent application Ser. No.12/558,184, filed Sep. 11, 2009, now U.S. Pat. No. 8,727,042, issued May20, 2014, the disclosures of each of which are hereby incorporatedherein in their entireties by this reference. This application isrelated to U.S. patent application Ser. No. 12/852,313, filed Aug. 6,2010, now U.S. Pat. No. 8,579,052, issued Nov. 12, 2013, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/232,265,filed Aug. 7, 2009; and this application is also related to U.S. patentapplication Ser. No. 12/901,253, filed Oct. 8, 2010, now U.S. Pat. No.8,496,076, issued Jul. 30, 2013, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/252,049, filed Oct. 15, 2009;and this application is also related to U.S. patent application Ser. No.13/226,127, filed Sep. 6, 2011, now U.S. Pat. No. 8,800,693, issued Aug.12, 2014, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/411,355, filed Nov. 8, 2010. This application isalso related to U.S. patent application Ser. No. 14/030,820, filed Sep.18, 2013, and U.S. patent application Ser. No. 13/904,590, filed May 29,2013, now U.S. Pat. No. 9,388,640, issued Jul. 12, 2016.

FIELD

The present invention relates generally to polycrystalline compacts,which may be used, for example, as cutting elements for earth-boringtools, and to methods of forming such polycrystalline compacts, cuttingelements, and earth-boring tools.

BACKGROUND

Earth-boring tools for forming wellbores in subterranean earthformations generally include a plurality of cutting elements secured toa body. For example, fixed-cutter earth-boring rotary drill bits (alsoreferred to as “drag bits”) include a plurality of cutting elements thatare fixedly attached to a bit body of the drill bit. Similarly, rollercone earth-boring rotary drill bits may include cones that are mountedon bearing pins extending from legs of a bit body such that each cone iscapable of rotating about the bearing pin on which it is mounted. Aplurality of cutting elements may be mounted to each cone of the drillbit. In other words, earth-boring tools typically include a bit body towhich cutting elements are attached.

The cutting elements used in such earth-boring tools often includepolycrystalline diamond compacts (often referred to as “PDC”), which actas cutting faces of a polycrystalline diamond material. Polycrystallinediamond material is material that includes interbonded grains orcrystals of diamond material. In other words, polycrystalline diamondmaterial includes direct, inter-granular bonds between the grains orcrystals of diamond material. The terms “grain” and “crystal” are usedsynonymously and interchangeably herein.

Polycrystalline diamond compact cutting elements are typically formed bysintering and bonding together relatively small diamond grains underconditions of high temperature and high pressure in the presence of acatalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) toform a layer (e.g., a compact or “table”) of polycrystalline diamondmaterial on a cutting element substrate. These processes are oftenreferred to as high temperature/high pressure (HTHP) processes. Thecutting element substrate may comprise a cermet material (i.e., aceramic-metal composite material) such as, for example, cobalt-cementedtungsten carbide. In such instances, the cobalt (or other catalystmaterial) in the cutting element substrate may be swept into the diamondgrains during sintering and serve as the catalyst material for formingthe inter-granular diamond-to-diamond bonds, and the resulting diamondtable, from the diamond grains. In other methods, powdered catalystmaterial may be mixed with the diamond grains prior to sintering thegrains together in a HTHP process.

Upon formation of a diamond table using a HTHP process, catalystmaterial may remain in interstitial spaces between the grains of diamondin the resulting polycrystalline diamond compact. The presence of thecatalyst material in the diamond table may contribute to thermal damagein the diamond table when the cutting element is heated during use, dueto friction at the contact point between the cutting element and theformation.

Polycrystalline diamond compact cutting elements in which the catalystmaterial remains in the polycrystalline diamond compact are generallythermally stable up to a temperature of about seven hundred fiftydegrees Celsius (750° C.), although internal stress within the cuttingelement may begin to develop at temperatures exceeding about threehundred fifty degrees Celsius (350° C.). This internal stress is atleast partially due to differences in the rates of thermal expansionbetween the diamond table and the cutting element substrate to which itis bonded. This differential in thermal expansion rates may result inrelatively large compressive and tensile stresses at the interfacebetween the diamond table and the substrate, and may cause the diamondtable to delaminate from the substrate. At temperatures of about sevenhundred fifty degrees Celsius (750° C.) and above, stresses within thediamond table itself may increase significantly due to differences inthe coefficients of thermal expansion of the diamond material and thecatalyst material within the diamond table. For example, cobaltthermally expands significantly faster than diamond, which may causecracks to form and propagate within the diamond table, eventuallyleading to deterioration of the diamond table and ineffectiveness of thecutting element.

Furthermore, at temperatures at or above about seven hundred fiftydegrees Celsius (750° C.), some of the diamond crystals within thepolycrystalline diamond compact may react with the catalyst materialcausing the diamond crystals to undergo a chemical breakdown orback-conversion to another allotrope of carbon or another carbon-basedmaterial. For example, the diamond crystals may graphitize at thediamond crystal boundaries, which may substantially weaken the diamondtable. In addition, at extremely high temperatures, in addition tographite, some of the diamond crystals may be converted to carbonmonoxide and carbon dioxide.

In order to reduce the problems associated with differential rates ofthermal expansion and chemical breakdown of the diamond crystals inpolycrystalline diamond compact cutting elements, so-called “thermallystable” polycrystalline diamond compacts (which are also known asthermally stable products, or “TSPs”) have been developed. Such athermally stable polycrystalline diamond compact may be formed byleaching the catalyst material (e.g., cobalt) out from interstitialspaces between the interbonded diamond crystals in the diamond tableusing, for example, an acid or combination of acids (e.g., aqua regia).All of the catalyst material may be removed from the diamond table, orcatalyst material may be removed from only a portion thereof. Thermallystable polycrystalline diamond compacts in which substantially allcatalyst material has been leached out from the diamond table have beenreported to be thermally stable up to temperatures of about twelvehundred degrees Celsius (1200° C.). It has also been reported, however,that such fully leached diamond tables are relatively more brittle andvulnerable to shear, compressive, and tensile stresses than arenon-leached diamond tables. In addition, it is difficult to secure acompletely leached diamond table to a supporting substrate. In an effortto provide cutting elements having polycrystalline diamond compacts thatare more thermally stable relative to non-leached polycrystallinediamond compacts, but that are also relatively less brittle andvulnerable to shear, compressive, and tensile stresses relative to fullyleached diamond tables, cutting elements have been provided that includea diamond table in which the catalyst material has been leached from aportion or portions of the diamond table. For example, it is known toleach catalyst material from the cutting face, from the side of thediamond table, or both, to a desired depth within the diamond table, butwithout leaching all of the catalyst material out from the diamondtable.

BRIEF SUMMARY

In some embodiments, the present invention includes polycrystallinecompacts that comprise a plurality of grains of hard material having anaverage grain size of about five hundred nanometers (500 nm) or less.The plurality of grains of hard material are interspersed andinterbonded to form a polycrystalline hard material. The polycrystallinehard material has an interstitial material disposed in at least someinterstitial spaces between the plurality of grains of hard material.The interstitial material comprises at least one of a boride, a carbide,a nitride, a metal carbonate, a metal bicarbonate, and a non-catalyticmetal.

In additional embodiments, the present invention includespolycrystalline compacts comprising a first plurality of grains of hardmaterial having a first average grain size and at least a secondplurality of grains of hard material having a second average grainssize. The second average grain size of the at least a second pluralityof grains is at least about one hundred fifty (150) times larger thanthe first average grain size of the first plurality of grains. The firstplurality of grains and the at least a second plurality of grains areinterspersed and interbonded to form a polycrystalline hard material.The polycrystalline hard material may further include an interstitialmaterial disposed in at least some interstitial spaces between the firstplurality of grains and the at least a second plurality of grains of thepolycrystalline hard material. The interstitial material comprises atleast one of a boride, a carbide, a nitride, a metal carbonate, a metalbicarbonate, and a non-catalytic metal.

Further embodiments of the present invention include cutting elementscomprising a polycrystalline compact on a substrate. The polycrystallinecompact comprises a plurality of interspersed and interbonded grains ofhard material that form a polycrystalline hard material. The interbondedgrains comprise a first plurality of grains having a first average grainsize and at least a second plurality of grains having a second averagegrain size at least one hundred fifty (150) times larger than the firstaverage grain size of the first plurality of grains. The polycrystallinecompact may further include an interstitial material disposed in atleast some interstitial spaces between the interbonded grains of thepolycrystalline hard material. The interstitial material comprises atleast one of a boride, a carbide, a nitride, a metal carbonate, a metalbicarbonate, and a non-catalytic metal.

Additional embodiments of the present invention include earth-boringdrill bits that have a bit body and a plurality of cutting elementsattached to the bit body. At least one cutting element of the pluralitycomprises a hard polycrystalline material that includes a firstplurality of grains having a first average particle size, and at least asecond plurality of grains having a second average particle size atleast one hundred fifty (150) times larger than the first averageparticle size of the first plurality of grains. The first plurality ofgrains and the second plurality of grains are interspersed andinterbonded to form the polycrystalline hard material. An interstitialmaterial may be disposed in at least some interstitial spaces betweenthe interspersed and interbonded grains of the polycrystalline hardmaterial. The interstitial material comprises at least one of a boride,a carbide, a nitride, a metal carbonate, a metal bicarbonate, and anon-catalytic metal.

Additional embodiments of the present invention include methods ofmaking a polycrystalline compact. The methods include at least partiallycoating each nanoparticle of a plurality of nanoparticles of hardmaterial with a coating material comprising at least one of a boride, acarbide, a nitride, a metal carbonate, a metal bicarbonate, and anon-catalytic metal. The nanoparticles are sintered to form apolycrystalline hard material comprising a plurality of grains formedfrom the plurality of nanoparticles. The plurality of grains areinterspersed and interbonded to form the polycrystalline hard material

Still further embodiments of the present invention include methods ofmaking a polycrystalline compact. The methods include at least partiallycoating each particle of a first plurality of particles having a firstaverage particle size with a coating material comprising at least one ofa boride, a carbide, a nitride, a metal carbonate, a metal bicarbonate,and a non-catalytic metal. The coated first plurality of particles aredispersed among at least a second plurality of particles having a secondaverage particle size that is larger than the first average particlesize of the first plurality of particles, and the first plurality ofparticles and the at least a second plurality of particles are sinteredto form a polycrystalline hard material that includes a first pluralityof grains formed from the first plurality of particles and a secondplurality of grains formed from the second plurality of particles. Thefirst plurality of grains and the second plurality of grains areinterspersed and interbonded to form the polycrystalline hard material.The first average particle size of the first plurality of particles andthe second average particle size of the second plurality of particlesmay be selected to cause the second plurality of grains to have a secondaverage grain size at least about one hundred fifty (150) times largerthan a first average grain size of the first plurality of grains.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of the presentinvention, various features and advantages of embodiments of theinvention may be more readily ascertained from the following descriptionof some embodiments of the invention when read in conjunction with theaccompanying drawings, in which:

FIG. 1A is a partial cut-away perspective view illustrating anembodiment of a cutting element comprising a polycrystalline compact ofthe present invention;

FIG. 1B is a simplified drawing showing how a microstructure of thepolycrystalline compact of FIG. 1A may appear under magnification, andillustrates interbonded and interspersed larger and smaller grains ofhard material;

FIG. 2 is a simplified drawing of a coated nanoparticle that may be usedto form a polycrystalline compact like that of FIGS. 1A and 1B inaccordance with some embodiments of methods of the present invention;

FIG. 3 is a simplified drawing of another coated nanoparticle that maybe used to form a polycrystalline compact like that of FIGS. 1A and 1Bin accordance with some embodiments of methods of the present invention;and

FIG. 4 is a perspective view of an embodiment of a fixed-cutterearth-boring rotary drill bit that includes a plurality ofpolycrystalline compacts like that shown in FIGS. 1A and 1B.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of anyparticular polycrystalline compact, microstructure of a polycrystallinecompact, particle, cutting element, or drill bit, and are not drawn toscale, but are merely idealized representations employed to describe thepresent invention. Additionally, elements common between figures mayretain the same numerical designation.

As used herein, the term “drill bit” means and includes any type of bitor tool used for drilling during the formation or enlargement of awellbore and includes, for example, rotary drill bits, percussion bits,core bits, eccentric bits, bicenter bits, reamers, mills, drag bits,roller cone bits, hybrid bits and other drilling bits and tools known inthe art.

As used herein, the term “fullerene” means and includes cage-like hollowmolecules comprising a plurality of carbon atoms bonded together in apolyhedral structure. Fullerenes may include, for example, between abouttwenty (20) and about one hundred (100) carbon atoms. For example, C₆₀is a fullerene having sixty (60) carbon atoms, and is a relativelycommon, commercially available fullerene. Other fullerenes include, forexample, C₃₀, C₃₂, C₃₄, C₃₈, C4₄₀, C₄₂, C₄₄, C₄₆, C₄₈, C₅₀, C₅₂, andC₇₀.

As used herein, the term “nanoparticle” means and includes any particlehaving an average particle diameter of about 500 nm or less.

As used herein, the term “carbon compound” means and includes anymaterial comprising two or more chemical elements, one of which iscarbon, that together form a generally crystalline substance having adefined chemical composition. Carbon compounds do not include pureallotropes (e.g., diamond, graphite, amorphous carbon,buckminsterfullerenes, etc.), which comprise only the element of carbon.Carbides are carbon compounds.

As used herein, the term “polycrystalline material” means and includesany material comprising a plurality of grains or crystals of thematerial that are bonded directly together by inter-granular bonds. Thecrystal structures of the individual grains of the material may berandomly oriented in space within the polycrystalline material.

As used herein, the term “polycrystalline compact” means and includesany structure comprising a polycrystalline material formed by a processthat involves application of pressure (e.g., compaction) to theprecursor material or materials used to form the polycrystallinematerial.

As used herein, the term “inter-granular bond” means and includes anydirect atomic bond (e.g., covalent, metallic, etc.) between atoms inadjacent grains of material.

As used herein, the term “diamondoid” means and includes the carbon cagemolecule known as adamantane (C₁₀H₁₆), which is the smallest unit cagestructure of the diamond crystal lattice, as well as variants ofadamantane (e.g., molecules in which other atoms (e.g., N, O, Si, or S)are substituted for carbon atoms in the molecule) and carbon cagepolymantane molecules including between two (2) and about twenty (20)adamantane cages per molecule (e.g., diamantane, triamantane,tetramantane, pentamantane, hexamantane, heptamantane, etc.).

As used herein, the term “catalyst material” refers to any material thatis capable of substantially catalyzing the formation of inter-granularbonds between grains of hard material during an HTHP process. Forexample, catalyst materials for diamond include cobalt, iron, nickel,other elements from Groups 8, 9, or 10 of the Periodic Table of theElements, and alloys thereof.

As used herein, the term “non-catalytic metal” refers to any metal ormetal alloy that is not a catalyst material.

As used herein, the term “hard material” means and includes any materialhaving a Knoop hardness value of about 3,000 Kg_(f)/mm² (29,420 MPa) ormore. Hard materials include, for example, diamond and cubic boronnitride.

FIG. 1A is a simplified, partially cut-away perspective view of anembodiment of a cutting element 10 of the present invention. The cuttingelement 10 comprises a polycrystalline compact in the form of a layer ofhard polycrystalline material 12, also known in the art as apolycrystalline table, that is provided on (e.g., formed on or attachedto) a supporting substrate 16 with an interface 14 therebetween. Thoughthe cutting element 10 in the embodiment depicted in FIG. 1A iscylindrical or disc-shaped, in other embodiments, the cutting element 10may have any desirable shape, such as a dome, cone, chisel, etc.

In some embodiments, the polycrystalline material 12 comprisespolycrystalline diamond. In such embodiments, the cutting element 10 maybe referred to as a polycrystalline diamond compact (PDC) cuttingelement. In other embodiments, the polycrystalline material 12 maycomprise another hard material such as, for example, polycrystallinecubic boron nitride.

FIG. 1B is an enlarged view illustrating how a microstructure of thepolycrystalline material 12 of the cutting element 10 may appear undermagnification. As discussed in further detail below, the polycrystallinematerial 12 includes at least some grains of hard material that have anaverage grain size of about five hundred nanometers (500 nm) or less(e.g., between about one nanometer (1 nm) and about one hundred fiftynanometers (150)). Thus, at least some grains of hard material in themicrostructure of the polycrystalline material 12 may be nanoparticles.

As shown in FIG. 1B, the grains of the polycrystalline material 12 mayhave a multi-modal (e.g., bi-modal, tri-modal, etc.) grain sizedistribution. In other words, the layer of hard polycrystalline material12 includes a first plurality of grains 18 of hard material having afirst average grain size, and at least a second plurality of grains 20of hard material having a second average grain size that differs fromthe first average grain size of the first plurality of grains 18.

For example, the second plurality of grains 20 may be larger than thefirst plurality of grains 18. For example, the average grain size of thelarger grains 20 may be at least about one hundred fifty (150) timesgreater than the average grain size of the smaller grains 18. Inadditional embodiments, the average grain size of the larger grains 20may be at least about five hundred (500) times greater than the averagegrain size of the smaller grains 18. In yet further embodiments, theaverage grain size of the larger grains 20 may be at least about sevenhundred fifty (750) times greater than the average grain size of thesmaller grains 18. The smaller grains 18 and the larger grains 20 may beinterspersed and interbonded to form the layer of hard polycrystallinematerial 12. In other words, in embodiments in which the polycrystallinematerial 12 comprises polycrystalline diamond, the smaller grains 18 andthe larger grains 20 may be mixed together and bonded directly to oneanother by inter-granular diamond-to-diamond bonds 26 (represented bydashed lines in FIG. 1B).

As known in the art, the average grain size of grains within amicrostructure may be determined by measuring grains of themicrostructure under magnification. For example, a scanning electronmicroscope (SEM), a field emission scanning electron microscope (FESEM),or a transmission electron microscope (TEM) may be used to view or imagea surface of a polycrystalline material 12 (e.g., a polished and etchedsurface of the polycrystalline material 12). Commercially availablevision systems are often used with such microscopy systems, and thesevision systems are capable of measuring the average grain size of grainswithin a microstructure.

By way of example and not limitation, in embodiments in which theaverage grain size of the smaller grains 18 is between about onenanometer (1 nm) and about one hundred fifty nanometers (150 nm), theaverage grain size of the larger grains 20 may be between about fivemicrons (5 μm) and about forty microns (40 μm). Thus, in someembodiments, the ratio of the average grain size of the larger grains 20to the average grain size of the smaller grains 18 may be between about33:1 and about 40,000:1.

The large difference in the average grain size between the smallergrains 18 and the larger grains 20 may result in smaller interstitialspaces 22 or voids (represented as shaded areas in FIG. 1B) within themicrostructure of the polycrystalline material 12 (relative toconventional polycrystalline materials), and the total volume of theinterstitial spaces 22 or voids may be more evenly distributedthroughout the microstructure of the polycrystalline material 12. As aresult, any material present within the interstitial spaces 22 (e.g., acarbon compound or a catalyst material, as described below) may also bemore evenly distributed throughout the microstructure of thepolycrystalline material 12 within the relatively smaller interstitialspaces 22 therein.

In some embodiments, the number of smaller grains 18 per unit volume ofthe polycrystalline material 12 may be higher than the number of largergrains 20 per unit volume of the polycrystalline material 12.

The smaller grains 18 may comprise between about one-half of one percent(0.5%) and about thirty percent (30%) by volume of the polycrystallinematerial 12. More specifically, the smaller grains 18 may comprisebetween about one-half of one percent (0.5%) and about ten percent (10%)by volume of the polycrystalline material 12, or even between aboutone-half of one percent (0.5%) and about five percent (5%) by volume ofthe polycrystalline material 12. The remainder of the volume of thepolycrystalline material 12 may be substantially comprised by the largergrains 20. A relatively small percentage of the remainder of the volumeof the polycrystalline material 12 (e.g., less than about ten percent(10%)) may comprise interstitial spaces 22 between the smaller grains 18and the larger grains 20, which spaces may be at least partially filledwith a interstitial material 34 and a catalyst material 24, as describedbelow.

The interstitial spaces 22 interspersed throughout the microstructure ofthe polycrystalline material 12 between the smaller grains 18 and thelarger grains 20 may have an interstitial material 34 disposed thereinthat originates from a coating (not shown in FIG. 1B) disposed on thesmaller grains 18 prior to fabrication of the polycrystalline material12. The coating material that is originally present on the smallergrains 18 may ultimately reside in the interstitial spaces 22 afterfabrication of the polycrystalline material 12. The interstitialmaterial 34 may comprise at least one of a boride, a carbide, a nitride,a metal carbonate (e.g., calcium carbonate, magnesium carbonate,strontium carbonate, barium carbonate, etc.), a metal bicarbonate, and anon-catalytic metal. For example, the interstitial material 34 maycomprise a metal carbide such as silicon carbide, titanium carbide,tungsten carbide, tantalum carbide, etc., in some embodiments. Inadditional embodiments, the interstitial material 34 may comprise acarbon nitride material or a carbon boride material.

In some embodiments, the polycrystalline material 12 may also include acatalyst material 24 disposed in interstitial spaces 22 between thesmaller grains 18 and the larger grains 20 of the polycrystalline hardmaterial. The catalyst material 24 may comprise a catalyst material 24capable of (and used to) catalyze the formation of the inter-granularbonds 26 between the grains of the smaller grains 18 and the largergrains 20 of the polycrystalline material 12. In other embodiments,however, the interstitial spaces 22 between the smaller grains 18 andthe larger grains 20 in some or all regions of the polycrystallinematerial 12 may be at least substantially free of such a catalystmaterial 24. In such embodiments, the interstitial spaces 22 maycomprise voids filled with gas (e.g., air), in addition to anyinterstitial material 34 present therein.

In embodiments in which the polycrystalline material 12 comprisespolycrystalline diamond, the catalyst material 24 may comprise a Group8, 9, or 10 element (e.g., iron, cobalt, or nickel) or an alloy thereof,and the catalyst material 24 may comprise between about one half of onepercent (0.1%) and about ten percent (10%) by volume of the hardpolycrystalline material 12. In additional embodiments, the catalystmaterial 24 may comprise a carbonate material such as, for example, acarbonate of one or more of magnesium, calcium, strontium, and barium.Carbonates may also be used to catalyze the formation of polycrystallinediamond. Accordingly, the interstitial material 34 may also act as acatalyst material 24 in some embodiments of the invention.

The layer of hard polycrystalline material 12 of the cutting element 10may be formed using a high temperature/high pressure (HTHP) process.Such processes, and systems for carrying out such processes, aregenerally known in the art. In some embodiments, the polycrystallinematerial 12 may be formed on a supporting substrate 16 (as shown in FIG.1A) of cemented tungsten carbide or another suitable substrate materialin a conventional HTHP process of the type described, by way ofnon-limiting example, in U.S. Pat. No. 3,745,623 to Wentorf et al.(issued Jul. 17, 1973), or may be formed as a freestandingpolycrystalline material 12 (i.e., without the supporting substrate 16)in a similar conventional HTHP process as described, by way ofnon-limiting example, in U.S. Pat. No. 5,127,923 Bunting et al. (issuedJul. 7, 1992), the disclosure of each of which patents is incorporatedherein in its entirety by this reference. In some embodiments, thecatalyst material 24 may be supplied from the supporting substrate 16during an HTHP process used to form the polycrystalline material 12. Forexample, the substrate 16 may comprise a cobalt-cemented tungstencarbide material. The cobalt of the cobalt-cemented tungsten carbide mayserve as the catalyst material 24 during the HTHP process.

To form the polycrystalline material 12 in an HTHP process, aparticulate mixture comprising larger particles of hard material, aswell as coated, smaller nanoparticles of hard material (as described indetail below) may be subjected to elevated temperatures (e.g.,temperatures greater than about one thousand degrees Celsius (1,000°C.)) and elevated pressures (e.g., pressures greater than about fivegigapascals (5.0 GPa)) to form inter-granular bonds 26 between theparticles, thereby forming the larger grains 20 and the smaller grains18 of the polycrystalline material 12 from the larger and smallerparticles, respectively. In some embodiments, the particulate mixturemay be subjected to a pressure greater than about six gigapascals (6.0GPa) and a temperature greater than about one thousand five hundreddegrees Celsius (1,500° C.) in the HTHP process.

The time at the elevated temperatures and pressures may be relativelyshort when compared to conventional HTHP processes to prevent the atomsof the smaller grains 18 from diffusing to, and being incorporated into,the larger grains 20. For example, in some embodiments, the particulatemixture may be subjected to a pressure greater than about sixgigapascals (6.0 GPa) and a temperature greater than about one thousandfive hundred degrees Celsius (1,500° C.) for less than about two minutes(2.0 min) during the HTHP process.

In embodiments in which a carbonate catalyst material 24 (e.g., acarbonate of one or more of magnesium, calcium, strontium, and barium)is used to catalyze the formation of polycrystalline diamond, theparticulate mixture may be subjected to a pressure greater than aboutseven point seven gigapascals (7.7 GPa) and a temperature greater thanabout two thousand degrees Celsius (2,000° C.).

The particulate mixture may comprise particles for forming the largergrains 20 previously described herein. The particulate mixture may alsocomprise particles of catalyst material 24. In some embodiments, theparticulate mixture may comprise a powder-like substance. In otherembodiments, however, the particulate mixture may be carried by (e.g.,on or in) another material, such as a paper or film, which may besubjected to the HTHP process.

The particulate mixture may also comprise smaller particles (e.g.,nanoparticles) for forming the smaller grains 18 previously describedherein, which may be provided as coated nanoparticles 28 like that shownin the simplified illustration of FIG. 2. The coated nanoparticles 28may comprise nanoparticles 30 of a hard material that are at leastpartially coated with a coating material 37 prior to being subjected tothe HTHP process. In embodiments in which the polycrystalline material12 includes polycrystalline diamond, the nanoparticles 30 may comprise,for example, diamond or diamondoid nanocrystals.

As previously mentioned, the coating material 37 corresponds to, and mayultimately form, the interstitial material 34 previously described withreference to FIG. 1B. Thus, the coating material 37 may comprise atleast one of a boride, a carbide, a nitride, a metal carbonate (e.g.,calcium carbonate, magnesium carbonate, strontium carbonate, bariumcarbonate, etc.), a metal bicarbonate, and a non-catalytic metal. Forexample, the coating material 37 may comprise a metal carbide such assilicon carbide, titanium carbide, tungsten carbide, tantalum carbide,etc., in some embodiments. In additional embodiments, the coatingmaterial 37 may comprise a carbon nitride material or a carbon boridematerial. Nitrogen and boron are elements known to diffuse readily incertain hard materials, such as diamond. Thus in some embodiments,elements of the coating material 37 may migrate to, and diffuse within,the smaller grains 18, the larger grains 20, or to both the smallergrains 18 and the larger grains 20 during an HTHP process used to formthe polycrystalline material 12, without adversely affecting thephysical properties of the polycrystalline material 12 in anysignificant manner.

By way of example and not limitation, processes such as liquid sol-gel,flame spray pyrolysis, chemical vapor deposition (CVD), physical vapordeposition (PVD) (e.g., sputtering), and atomic layer deposition (ALD),may be used to provide the coating material 37 on the nanoparticles 30.Other techniques that may be used to provide the coating material 37 onthe nanoparticles 30 include colloidal coating processes, plasma coatingprocesses, microwave plasma coating processes, physical admixtureprocesses, van der Waals coating processes, and electrophoretic coatingprocesses. In some embodiments, coating material 37 may be provided onthe nanoparticles 30 in a fluidized bed reactor.

As known in the art, nanoparticles 30 of diamond or diamondoid crystalstypically comprise a relatively thin carbon-based, non-diamond outerlayer or shell. Such a shell may comprise, for example, amorphouscarbon, and is often referred to in the art as a “carbon onion.” Inaccordance with some embodiments of the present invention, such acarbon-based, non-diamond outer layer or shell on the nanoparticles 30may be at least partially replaced with a coating material 37 by, forexample, reacting the carbon of the carbon-based, non-diamond outerlayer or shell with one or more additional elements to form the coatingmaterial 37, or by removing the non-diamond outer layer or shell on thenanoparticles 30 and subsequently depositing the coating material 37over the nanoparticles 30.

In some embodiments, coated nanoparticles 28 like that shown in FIG. 2may be formed by nitriding (reacting nitrogen with) or boriding(reacting boron with) the relatively thin carbon-based, non-diamondouter layer or shell of nanoparticles 30 of diamond or diamondoidcrystals to form a carbon nitride or a carbon boride coating material37.

In further embodiments, coated nanoparticles 28 like that shown in FIG.2 may be formed by depositing a non-catalytic metal over nanoparticles30 of diamond or diamondoid crystals to form a non-catalytic metalcoating material 37.

In additional embodiments, coated nanoparticles 28 like that shown inFIG. 2 may be formed by at least partially coating the nanoparticles 30with a reagent material capable of reacting with carbon to form thecoating material 37, and reacting the reagent material with carbon atomsin or on each of the nanoparticles 30 to form the coating material 37,as described below with reference to FIG. 3.

FIG. 3 illustrates a multi-layer coated nanoparticle 28′ that includes adiamond nanoparticle 30, a non-diamond carbon shell 32 at leastpartially coating the diamond nanoparticle 30, and a layer of reagentmaterial 35 at least partially coating the carbon shell 32. Thus,although the carbon shell 32 and the reagent material 35 are depicted inFIG. 3 as completely encapsulating the nanoparticle 30, in otherembodiments, they may only partially coat the nanoparticle 30. Thediamond nanoparticle 30 may comprise a single diamond crystal or acluster of diamond crystals.

As previously mentioned, the reagent material 35 comprises a materialcapable of reacting with carbon atoms of the carbon shell 32 to form thecoating material 37 (FIG. 2). By way of example and not limitation, thereagent material 35 may comprise, for example, at least one of nitrogen,a nitrogen compound, a carbonate-forming metal, a metal carbonate, abicarbonate-forming metal, a metal bicarbonate, a carbide-forming metal,and a metal carbide.

The carbon shell 32 may react with the reagent material 35 to form thecoating material 37. In some embodiments, at least a portion of thenon-diamond carbon shell 32 may undergo a change in atomic structureduring or prior to sintering. Carbon atoms in the non-diamond carbonshell 32 may diffuse to and enter the diamond crystal structure of thediamond nanoparticle 30 (i.e., contribute to grain growth of the diamondnanoparticle 30). Some atoms of the non-diamond carbon shell 32 may alsobe incorporated into the larger grains 20, or may nucleate and formadditional, new smaller grains 18.

The coated nanoparticles 28 and the diamond nanoparticles 30 may have anaverage particle size selected to cause the average grain size of thesmaller grains 18 (formed from the diamond nanoparticles 30) to bebetween about one nanometer (1 nm) and about one hundred fiftynanometers (150 nm). Furthermore, as previously mentioned, theparticulate mixture used to form the polycrystalline material 12 mayfurther comprise particles for forming the larger grains 20. The averageparticle size of these relatively larger particles may be selected tocause the average grain size of the larger grains 20 (formed from therelatively larger particles) to be between about five microns (5 μm) andabout forty microns (40 μm). The average thickness of the carbon shell32 and the resulting coating material 37 layer may be selected dependentupon the particular material compositions of these layers, as well as onthe desired final composition and microstructure of the polycrystallinematerial 12.

Multi-layer coated nanoparticles 28′ like that shown in FIG. 3 may beformed by providing (e.g., depositing, growing, forming, etc.) reagentmaterial 35 on the nanoparticles 30, which may have a naturallyoccurring non-diamond carbon shell 32 thereon. The process used toprovide the reagent material 35 on the nanoparticles 30 will depend uponthe particular composition of the reagent material 35 to be provided onthe nanoparticles 30. By way of example and not limitation, processessuch as liquid sol-gel, flame spray pyrolysis, chemical vapor deposition(CVD), physical vapor deposition (PVD) (e.g., sputtering), and atomiclayer deposition (ALD), may be used to provide the reagent material 35on the nanoparticles 30. Other techniques that may be used to providethe reagent material 35 on the nanoparticles 30 include colloidalcoating processes, plasma coating processes, microwave plasma coatingprocesses, physical admixture processes, van der Waals coatingprocesses, and electrophoretic coating processes. In some embodiments,the non-diamond carbon shell 32 and the reagent material 35 may beprovided on the nanoparticles 30 in a fluidized bed reactor.

If the nanoparticle 30 does not have a naturally occurring non-diamondcarbon shell 32 thereon, the non-diamond carbon shell 32 may be formedon the nanoparticle 30 by, for example, heating the nanoparticle 30 toan elevated temperature and causing an outer region of the diamondnanoparticle 30 to decompose from diamond to a carbon-based, non-diamondmaterial such as amorphous carbon.

In some embodiments, the reagent material 35 may react with thenon-diamond carbon shell 32 to form the coating material 37 as thereagent material 35 is deposited on the carbon shell 32 without any needfor further processing to initiate the reaction therebetween. In suchembodiments, multi-layer coated nanoparticles 28′ like that of FIG. 3may be transient in nature, such that they are not formed or stable forany significant period of time, and coated nanoparticles 28 like thatshown in FIG. 2 may simply form as the reagent material 35 is depositedover the non-diamond carbon shell 32. In other embodiments, however, thereagent material 35 may not react with the non-diamond carbon shell 32to form the coating material 37 without further processing. In otherwords, multi-layer coated nanoparticles 28′ like that of FIG. 3 may formupon deposition of the reagent material 35, and the multi-layer coatednanoparticles 28′ may subsequently be subjected to one or more of aselected temperature, pressure, and atmosphere to cause the reagentmaterial 35 and the non-diamond carbon shell 32 to react with oneanother to form the coating material 37. Furthermore, in someembodiments, the reagent material 35 and the non-diamond carbon shell 32may react with one another during an HTHP process used to form thepolycrystalline material 12 from a particulate mixture including themulti-layer coated nanoparticles 28′.

In additional embodiments, the coated nanoparticle 28 of FIG. 2 maycomprise a nanoparticle 30 and a coating material that is not reactivewith the nanoparticle 30. For example, in embodiments in which thenanoparticle 30 comprises diamond and has an outer non-diamond carbonshell 32 (FIG. 3), the coating material may comprise a material thatwill not react with the nanoparticle 30 or the non-diamond carbon shell32, but that will thermally stabilize the nanoparticle 30 during an HTHPprocess used to form a polycrystalline material 12, as discussed infurther detail below.

As previously mentioned, a particulate mixture that includes relativelysmaller particles (e.g., coated particles like the coated particle 28 ofFIG. 2 or multi-layer coated particles 28′ like that of FIG. 3) forforming the smaller grains 18, relatively larger particles for formingthe larger grains 20, and, optionally, a catalyst material 24 (forcatalyzing the formation of inter-granular bonds 26 between the smallergrains 18 and the larger grains 20) may be subjected to an HTHP processto form a polycrystalline material 12. After the HTHP process, catalystmaterial 24 (e.g., cobalt) may be disposed in at least some of theinterstitial spaces 22 between the interbonded smaller grains 18 andlarger grains 20. During the HTHP process, at least some of the coatingmaterial 37 on the smaller particles may be displaced or diffuse duringthe HTHP process to allow the formation of inter-granular bonds 26between the nanoparticles 30 and the relatively larger particles of hardmaterial. After the HTHP process, the coating material 37 may also bedisposed in at least some of the interstitial spaces 22 between thesmaller grains 18 and the larger grains 20 of the polycrystallinematerial 12, and, thus, may be characterized as the interstitialmaterial 34 previously described herein with reference to FIG. 1B.

Optionally, the catalyst material 24, the interstitial material 34, orboth the catalyst material 24 and the interstitial material 34 may beremoved from the polycrystalline material 12 after the HTHP process, asis known in the art. For example, a leaching process may be used toremove the catalyst material 24 and/or the interstitial material 34 fromthe interstitial spaces 22 between the interbonded smaller grains 18 andlarger grains 20 of the polycrystalline material 12. By way of exampleand not limitation, the polycrystalline material 12 may be leached usinga leaching agent and process such as those described more fully in, forexample, U.S. Pat. No. 5,127,923 to Bunting et al. (issued Jul. 7,1992), and U.S. Pat. No. 4,224,380 to Bovenkerk et al. (issued Sep. 23,1980), the disclosure of each of which patent is incorporated herein inits entirety by this reference. Specifically, aqua regia (a mixture ofconcentrated nitric acid (HNO₃) and concentrated hydrochloric acid(HCl)) may be used to at least substantially remove catalyst material 24and/or interstitial material 34 from the interstitial spaces 22. It isalso known to use boiling hydrochloric acid (HCl) and boilinghydrofluoric acid (HF) as leaching agents. One particularly suitableleaching agent is hydrochloric acid (HCl) at a temperature of above onehundred ten degrees Celsius (110° C.), which may be provided in contactwith the polycrystalline material 12 for a period of about two (2) hoursto about sixty (60) hours, depending upon the size of the bodycomprising the polycrystalline material 12. After leaching thepolycrystalline material 12, the interstitial spaces 22 between theinterbonded smaller grains 18 and larger grains 20 within thepolycrystalline material 12 may be at least substantially free ofcatalyst material 24 used to catalyze formation of inter-granular bonds26 between the grains in the polycrystalline material 12, and may be atleast substantially free of interstitial material 34. Furthermore, onlya portion of the polycrystalline material 12 may be subjected to theleaching process, or the entire body of the polycrystalline material 12may be subjected to the leaching process.

Embodiments of cutting elements 10 of the present invention that includea polycrystalline compact comprising polycrystalline material 12 formedas previously described herein, such as the cutting element 10illustrated in FIG. 1A, may be formed and secured to an earth-boringtool such as, for example, a rotary drill bit, a percussion bit, acoring bit, an eccentric bit, a reamer tool, a milling tool, etc., foruse in forming wellbores in subterranean formations. As a non-limitingexample, FIG. 4 illustrates a fixed cutter type earth-boring rotarydrill bit 36 that includes a plurality of cutting elements 10, each ofwhich includes a polycrystalline compact comprising polycrystallinematerial 12 as previously described herein. The rotary drill bit 36includes a bit body 38, and the cutting elements 10, which includepolycrystalline compacts 12, are bonded to the bit body 38. The cuttingelements 10 may be brazed (or otherwise secured) within pockets formedin the outer surface of the bit body 38.

Polycrystalline hard materials having a relatively large difference inaverage grain size between a first plurality of relatively smallergrains and a second plurality of relatively larger grains, as describedhereinabove, may exhibit improved thermal stability, improved mechanicaldurability, or both improved thermal stability and improved mechanicaldurability relative to previously known polycrystalline hard materials.By surrounding the relatively larger grains with the relatively smallergrains, less catalyst material may be disposed in interstitial spacesbetween the grains in the ultimate polycrystalline hard material, whichmay improve one or both of the thermal stability and the mechanicaldurability of the polycrystalline hard material. Furthermore, asnanoparticles are relatively reactive compared to larger particles due,at least in part, to the high surface energy of the nanoparticles,nanoparticles of a hard material used to form the relatively smallergrains of hard material in the polycrystalline hard material may becoated, as described hereinabove, to improve the stability (e.g.,thermal stability) of the nanoparticles during an HTHP process used toform the polycrystalline hard material.

The foregoing description is directed to particular embodiments for thepurpose of illustration and explanation. It will be apparent, however,to one skilled in the art that many modifications and changes to theembodiments set forth above are possible without departing from thescope of the embodiments disclosed herein as hereinafter claimed,including legal equivalents. It is intended that the following claims beinterpreted to embrace all such modifications and changes.

What is claimed is:
 1. A polycrystalline compact, consisting essentiallyof: a plurality of grains of hard material, the grains comprising: afirst plurality of grains of hard material having a first average grainsize; at least a second plurality of grains of hard material having asecond average grain size that is at least about thirty-three (33) timeslarger than the first average grain size, the first plurality of grainsand the at least a second plurality of grains being interspersed andinterbonded to form a polycrystalline hard material; an interstitialmaterial comprising at least one material selected from the groupconsisting of calcium carbonate, strontium carbonate, barium carbonate,and metal bicarbonates; and an additional interstitial materialcomprising a catalyst material selected from the group consisting ofiron, nickel, cobalt, and alloys thereof; wherein the interstitialmaterial is concentrated around the first plurality of grains of hardmaterial.
 2. The polycrystalline compact of claim 1, wherein a ratio ofthe second average grain size to the first average grain size is betweenabout 33:1 and about 40,000:1.
 3. The polycrystalline compact of claim1, wherein the first average grain size is between about 1 nanometer (1nm) and about one hundred fifty nanometers (150 nm).
 4. Thepolycrystalline compact of claim 1, wherein the second average grainsize is between about five microns (5 μm) and about forty microns (40μm).
 5. The polycrystalline compact of claim 1, wherein the firstplurality of grains of hard material comprises between about one-half ofone percent (0.5%) and about thirty percent (30%) by volume of thepolycrystalline compact.
 6. The polycrystalline compact of claim 1,wherein the interstitial material comprises less than about ten percent(10%) by volume of the polycrystalline compact.
 7. The polycrystallinecompact of claim 1, wherein the first plurality of grains comprisesdiamond.
 8. The polycrystalline compact of claim 1, wherein the firstplurality of grains comprises cubic boron nitride.
 9. An earth-boringtool, comprising a body; and at least one cutting element attached tothe body, the at least one cutting element comprising a hardpolycrystalline material consisting essentially of: a plurality ofgrains of hard material, the grains comprising: a first plurality ofgrains of hard material having a first average grain size; at least asecond plurality of grains of hard material having a second averagegrain size that is at least about thirty-three (33) times larger thanthe first average grain size, the first plurality of grains and the atleast a second plurality of grains being interspersed and interbonded toform a polycrystalline hard material; an interstitial materialcomprising at least one material selected from the group consisting ofcalcium carbonate, strontium carbonate, barium carbonate, and metalbicarbonates; and an additional interstitial material comprising acatalyst material selected from the group consisting of iron, nickel,cobalt, and alloys thereof; wherein the interstitial material isconcentrated around the first plurality of grains of hard material. 10.The earth-boring tool of claim 9, wherein a ratio of the second averagegrain size to the first average grain size is between about 33:1 andabout 40,000:1.
 11. The earth-boring tool of claim 9, wherein the firstplurality of grains comprises diamond.
 12. The earth-boring tool ofclaim 9, wherein the first plurality of grains comprises cubic boronnitride.
 13. A particulate mixture for forming a polycrystallinecompact, the particulate mixture consisting essentially of: a pluralityof grains of hard material, the grains comprising: a first plurality ofgrains of hard material having a first average grain size and having acoating comprising at least one material selected from the groupconsisting of calcium carbonate, strontium carbonate, barium carbonate,and metal bicarbonates; and a second plurality of grains of hardmaterial having a second average grain size at least about thirty-three(33) times larger than the first average grain size, the secondplurality of grains being interspersed with the first plurality ofgrains; and a catalyst material selected from the group consisting ofiron, nickel, cobalt, and alloys thereof; wherein the coating isconcentrated around the first plurality of grains of hard material andseparates the first plurality of grains from the catalyst material;wherein the first plurality of grains comprises between about one-halfof one percent (0.5%) and about thirty percent (30%) by volume of theparticulate mixture.
 14. The particulate mixture of claim 13, whereinthe first average grain size is less than five hundred nanometers (500nm).
 15. The particulate mixture of claim 13, wherein each of the firstplurality of grains and the second plurality of grains comprises grainsof diamond.
 16. The particulate mixture of claim 13, wherein each of thefirst plurality of grains and the second plurality of grains comprisesgrains of cubic boron nitride.
 17. The polycrystalline compact of claim1, wherein the plurality of grains of hard material consists essentiallyof the first plurality of grains and the at least a second plurality ofgrains.